Melt processing thermoplastic polymers

The biodegradable polymer available in the market today in largest amounts is PEA. PEA is a melt-processible thermoplastic polymer based completely on renewable resources. The manufacture of PEA includes one fermentation step followed by several chemical transformations. The typical annually renewable raw material source is com starch, which is broken down to unrefined dextrose. This sugar is then subjected to a fermentative transformation to lactic acid (LA). Direct polycondensation of LA is possible, but usually LA is first chemically converted to lactide, a cyclic dimer of LA, via a PLA prepolymer. Finally, after purification, lactide is subjected to a ring-opening polymerization to yield PLA [13-17]. 

Because of the ease of formation of these flammable pyrolysis products, polyesters have LOI values of 20-22 vol% (see Table 2.4), and hence, burn readily and because of the styrene content, give heavy soot formation. As these resins are cured at room temperature, bromine-containing flame retardants, which would decompose in melt-processed, thermoplastic polymers, may be effectively used. 

M.P. Dillon, S.S. Woods, K.J. Fronek, C. Lavallee, S.E. Amos, K.D. Weilandt, H. Kaspar, B. Hirsch, K. Hintzer, and P.J. Scott, Polymer processing additive containing a multimodal fluoropolymer and melt processable thermoplastic polymer composition employing the same, US Patent 6 277 919, assigned to Dyneon LLC (Oakdale, MN), August 21,2001. 

Since the ions in ionic polymers are held by chemical bonds within a low dielectric medium consisting of a covalent polymer backbone material with which they are incompatible, the polymer backbone is forced into conformations that allow the ions to associate with each other. Because these ionic associations involve ions from different chains they behave as crosslinks, but because they are thermally labile they reversibly break down on heating. lonomers therefore behave as cross-Unked, yet melt-processable, thermoplastic materials, or if the backbone is elastomeric, as thermoplastic rubbers. It should be noted that it is with the slightly ionic polymers, the ionomers, where the effect of ion aggregation is exploited to produce meltprocessable, specialist thermoplastic materials. With highly ionic polymers, the polyelectrolytes, the ionic cross-linking is so extreme that the polymers decompose on melting or are too viscous for use as thermoplastics. 

In the last two decades, numerous experimental and theoretical studies dealing with reaction-induced phase separation in multiphase polymer systems (mostly porous matrices, toughened plastics, melt processable thermoplastics [143], molecular composites, polymer dispersed liquid crystals, etc.) have been reported. A newcomer in this field should get acquainted with hundreds (possibly thousands) of papers and patents. The intention of this review was to provide a qualitative basis (quantitative occasionally) to rationalize the various factors that must be taken into account to obtain desired morphologies. 

Da Roz A.L., Carvalho A.J.F., Gandini A., Curvelo A.A.S. The effect of plasticizers on thermoplastic starch compositions obtained by melt processing, Carbohydr. Polym. 63 (2006) 417. 

The general term polysulfone describes an entire family of thermoplastic polymers which are melt processable. The polymers are particularly known for their toughness and stability at high temperatures. They contain the subunit aryl-S02-aryl, the defining feature of which is the sulfone group. This chapter will discuss blends of polysulfone polymers with other polymers, both thermoplastics and thermosets, and the results obtained from the production of such mixtures. 

EPDM-Derived Ionomers. Another type of ionomer containing sulfonate, as opposed to carboxyl anions, has been obtained by sulfonating ethylene—propjlene—diene (EPDM) mbbers (59,60). Due to the strength of the cross-link, these polymers are not inherently melt-processible, but the addition of other metal salts such as zinc stearate introduces thermoplastic behavior (61,62). These interesting polymers are classified as thermoplastic elastomers (see ELASTOLffiRS,SYNTHETIC-THERMOPLASTICELASTOLffiRS). 

The packaging (qv) requirements for shipping and storage of thermoplastic resins depend on the moisture that can be absorbed by the resin and its effect when the material is heated to processing temperatures. Excess moisture may result in undesirable degradation during melt processing and inferior properties. Condensation polymers such as nylons and polyesters need to be specially predried to very low moisture levels (3,4), ie, less than 0.2% for nylon-6,6 and as low as 0.005% for poly(ethylene terephthalate) which hydrolyzes faster. 

Deformation of a polymer melt—either thermoplastic or thermosetting. Processes operating in this way include extrusion, injection moulding and calendering, and form, in tonnage terms, the most important processing class. 

As with thermoplastics melt processes, the setting is achieved by cooling. It will be appreciated that such cooling is carried out while the polymer is under stress so that there is considerable frozen-in orientation. This can be maintained throughout the life of the article. It is possible with the higher molecular weight materials to heat shapes made from blanks many years previously and see them return to the original shape of the blank. 

A characteristic feature of thermoplastics shaped by melt processing operations is that on cooling after shaping many molecules become frozen in an oriented conformation. Such a conformation is unnatural to the polymer molecule, which continually strives to take up a randomly coiled state. If the molecules were unfrozen a stress would be required to maintain their oriented conformation. Another way of looking at this is to consider that there is a frozen-in stress corresponding to a frozen-in strain due to molecular orientation. 

Subsequently, much improved thermoplastic polyolefin rubbers were obtained by invoking a technique known as dynamic vulcanisation. This process has been defined (Coran, 1987) as the process of vulcanizing elastomer during its intimate melt-mixing with a non-vulcanizing thermoplastic polymer. Small elastomer droplets are vulcanized to give a particulate... 

---